IS 12843 limits deviations in the level (elevation), line/alignment and lateral position of erected members and the overall structure. Mis-aligned members force fit-up at connections (locked-in stresses), shift loads onto unintended eccentricities, and can foul cladding/services. The tolerances keep the assembled geometry within the IS 800 design and the cladding/interface requirements.
Key Requirements
•Level (elevation), line/alignment and lateral position deviations within the IS 12843 limits
•Mis-alignment beyond tolerance forces fit-up (locked-in stresses) and connection eccentricity
•Cumulative tolerance considered — individual member tolerances can stack to a non-fit
•Allow shop fabrication + rolling tolerances in connection detailing so erection can stay within limits
•Survey alignment/level before final bolting/welding; correct before lock-in
Practical Notes
✓Tolerances stack: in-tolerance individual members can still not fit if cumulative deviation isn't allowed for in connection detailing (cf. IS 12779/IS 1852).
✓Force-fitting mis-aligned members locks in stresses the design never saw — correct alignment before final connection, not after.
Common Mistakes
⚠Ignoring cumulative tolerance (individual members in spec, assembly won't fit).
⚠Force-fitting mis-aligned members (locked-in stresses).
⚠Final-bolting/welding before verifying level & alignment.